Method of making plastic embedded color-coded printed circuit



Nov. 1, 1966 M. TISCHLER 3,232,755

METHOD OF MAKING PLASTIC EMBEDDED COLOR-CODED PRINTED CIRCUIT Original Filed May 29. 1961 LARGE DRAWING OF cIRcuIT PATTERN PROOF NESSEISE YE W 4 PRINT DESIRED 5 MARKED SIZE FOR coLoR 5 SCHEME 6 PLI ALI T DE 5! l TRANSPARENCIES (ONE FOR EACH COLOR) EACH MODIFIED TO DELETE ALL BUT COLOR COMMON PARTS PI-IoTo-REsIsT SILK SCREENS I FOR EACH COLOR I II I)" I. lfi Fllsig SILK SCREEN STENCIL POLYESTER COPPER FOIL FILM ATTACHED usme COLORED ENAMELS To BACK WITH m coRREcT REGISTER RUBBER BASE AND BAKE ADHESIVE POLYESTER FILM ExPosED CEMENTED FACE DOWN ON coPPER THICK TRASPARENT PoIL PLASTIC BASE ETGHED ALLOW TRANSPARENT AWAY cEMENT TO SET STRIP OFF 5 DIScARD POLYESTER FILM cIRcuIT PATTERN REMAINS FILUSH MORRIS TISCHLER EMBEDDED IN BASE- coPPER SIDE ouT INVENTOR ATTORNEY United States Patent 3,282,755 METHOD OF MAKING PLASTIC EMBEDDED COLOR-CODEI) PRINTED CIRCUIT Morris Tischler, Baltimore, Md., assignor to Electronic Aids, Inc., Baltimore, Md., a corporation of Maryland Continuation of application Ser. No.

1961. This application June 14, 1965, Ser. No. 470,266

2 Claims. (Cl. 1563) This invention relates to electric conductors, and more particularly it pertains to a printed circuit article and process for manufacture thereof. This patent application is a continuation of US. patent application Serial No. 113,508 filed May 29, 1961 by applicant for Plastic Embedded Color-Coded Printed Circuit, now abandoned.

It is common practice in electronic apparatus to use colored wiring to facilitate the tracing of individual circuits. With the advent of printed circuitry, this color coding becomes even more desirable because of the involved paths by which circuits are routed in order to avoid crossovers. Then too, it is of great importance in the educational field to be able to explain circuit wiring of exhibition apparatus by reference to colors.

Accordingly, it is a principal object of this invention to provide a process for manufacturing plastic embedded color coded printed circuits.

Another object of this invention is to' provide a circuit board having a solderable flush embedded printed wiring pattern.

Still another object of this invention is to provide a protected printed circuit board which is both functional and decorative. 7

Yet another object of this invention is to provide colored printed circuit elements which are readily transferable to base structure thus protecting the base structure from etching fluids.

And still another object of the invention is to provide a circuit base for electronic apparatus which is easily traced by colors observable from the reverse side.

These and other objects and attendant advantages of this invention will become more readily apparent and understood from the following detailed specification and single sheet of accompanying drawings.

As shown in the drawing, the desired circuit is first laid out by an artist on a large scale drawing 1. A photo negative 2 is then made to the desired size of this large scale drawing 1.

From the photo negative, a proof print 3 is taken as well as a plurality of contact positive transparencies 6 equal in number to the different colors to be used.

The proof print 3 is marked as a guide to the colors desired, for example, the character image 4 to be yellow and the character image 5 to be red. Each positive transparency 6 is mechanically modified to delete all but the desired color common parts or characters.

Next, by a well-known photo-resist process, silk screen stencils 7 are made from each color-common modified positive transparency 6. Then using these stencils 7 sequentially in correct register colored enamel characters such as yellow enamel character 4a and red enamel characters 5a are applied to a common sheet of degreased copper foil 8 and baked for one-half hour at 140 degrees F.

A preferred enamel for this purpose includes a catalyst type silk screen ink with an added epoxy resin bonding agent. For example, uniglaze enamel with bonding agent Omega Research No. 803 has been found to be very successful. The degreasing of the copper foil 8 is best carried out in an ammonium persulphate solution which is effective in removing organic contamination.

A thin polyester film 9, such as mylar is now attached to the back of the stenciled and baked foil 8 using a rub- 113,508, May 29,

"ice

ber base adhesive and the assembly placed in an etching bath. All exposed copper is then dissolved away to the adhesive covered polyester film 9.

The yellow and red colored characters 4a and-5a remain unchanged but now have an underlying replica of themselves of copper foil 8 and are still positioned relative to each other on the polyester film 9.

This polyester film 9 is now cemented, character face down, onto a thick transparent plastic base 10 with a transparent cement suited to the plastic base material. For example, if plexiglass is chosen the most suitable cement would be Masco acrylic resin No. MC18.

After the cement has set and hardened, the polyester film 9 is stripped off and discarded. The characters 4a and 5a will be found flush embedded in the base 10 with the copper foil side exposed. The color side of each character 4a and 5a clearly shows through the transparent plastic and is protected against smudging from the fingers of a student or repairman.

The customary operations of drilling, eyeletting and soldering-in of components may be carried out through well-known techniques for ordinary printed circuits. It should be noted that the plastic base 10 is never exposed to etching fluid-s, thus preserving its dielectric property at a high level.

Obviously many modifications and variations of the present process and article of this invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A process for manufacturing a plastic embedded colored printed circuit pattern, comprising, applying colored enamel characters to a sheet of degreased copper foil, baking said sheet, attaching a thin flexible film to the back of said baked copper foil using an adhesive, etching said backed copper foil to dissolve the exposed copper and expose said thin flexible film with the col-ored characters remaining unchanged but having underlying replica of themselves of said copper foil and positioned relative to each other on said thin flexible film, cementing said thin flexible film character face down to a transparent plastic base material, and subsequently removing said thin flexible film, with said characters remaining embedded in said plastic base material with the copper foil side exposed and the colored characters visible on the reverse side thereof.

2. A process for manufacturing a plastic embedded colored printed circuit pattern, comprising, laying out a desired circuit pattern, making a photographic negative of a circuit pattern to the desired scale, making a plurality of contact positive transparencies from said photographic negative corresponding in number to the colors to be used in said printed circuit pattern, modifying each of said contact positive transparencies to delete all but the desired color common parts, making silk screen stencils of said color common modified positive transparencies, using said silk screen stencils sequentially in correct register to apply colored enamel characters to a common sheet of degreased copper foil, baking said sheet, attaching a polyester film to the back of the stenciled and baked copper foil using a rubber base adhesive, etching said polyester backed copper foil to dissolve the exposed copper and expose said adhesive covered polyester film with the colored characters remaining unchanged but having underlying replica of themselves of said copper foil and positioned relative to each other on said polyester film, cementing said polyester film character face down on to a transparent plastic base material, and subsequently removing said polyester film, with said characters remaining flush embedded in said plastic base matenial with the copper foil 3 4 side exposed and th: colored 2,628,998 2/1953 Frisbie 174-112 characters exposed on the reverse side thereof. 2, 92,190 10 1954 Pritikin 2,888,336 5/1959 Padgett 1563 References Cited y the Examiner 3,135,823 6/1964 Prifikin UNITED STATES PATENTS 5 3/ 1948 G taf 174 112 EARL M. BERGERT, Primary Examiner. 5/1948 Eisler 1563 HAROLD ANSHER, Examiner. 1/1949 Staehle 156--3 

1. A PROCESS FOR MANUFACTURING A PLASTIC EMBEDDED COLORED PRINTED CIRCUIT PATTERN, COMPRISING, APPLYING COLORED ENAMEL CHARACTERS TO A SHEET OF DEGREASED COPPER FOIL, BAKING SAID SHEET, ATTACHING A THIN FLEXIBLE FILM TO THE BACK OF SAID BAKED COPPER FOIL USING AN ADHESIVE, ETCHING SAID BACKED COPPER FOIL TO DISSOLVE THE EXPOSED COPPER AND EXPOSE SAID THIN FLEXIBLE FILM WITH THE COLORED CHARACTERS REMAINING UNCHANGED BUT HAVING UNDERLYING REPLICA OF THEMSELVES OF SAID COPPER FOIL AND POSITIONED RELATIVE TO EACH OTHER ON SAID THIN FLEXIBLE FILM, CEMENTING SAID THIN FLEXIBLE FILM CHARACTER FACE DOWN TO A TRANSPARENT PLASTIC BASE MATERIAL, AND SUBSEQUENTLY REMOVING SAID THIN FLEXIBLE FILM, WITH SAID CHARACTERS REMAINING EMBEDDED IN SAID PLASTIC BASE MATERIAL WITH THE COPPER FOIL 